1. Field of Invention
The invention relates to a blank for the production of a dental mould part and a holding device for the same.
Blanks of the type mentioned are used for producing inlays, onlays, crowns etc. in dentistry. The part in question is worked from the blank by milling or similar working techniques using a model taken from the prepared tooth or else, with numerical control, using a measurement of the tooth effected by optical or other means.
For this purpose, on account of the low work tolerances, a very precise and secure clamping of the blank in a holding device is necessary. In the event of reclamping following removal from the holding device for the purpose of checking or subsequent machining, it must be possible for the original position to be reproduced exactly.
2. Description of Related Art
A blank of the generic type is known (EP-A-0 160 797) in which a blank body is secured on a support which bears on the side facing away from the blank body an anchoring part of essentially circular cylindrical shape. However, it is only with difficulty that such an anchoring part can be clamped in a holding device rigidly and at the same time completely free of play, since, for instance, a similarly cylindrical receiving opening, which should permit the straightforward insertion of the anchoring part as far as a limit stop necessary for definition of the position in the axial direction and a likewise straightforward removal, must by necessity have a slightly greater diameter than the anchoring part. A resilient design of the parts of the holding device coming into contact with the blank, which design would in principle permit clamping free of play, can hardly be considered on account of the high precision requirements.